/* ----------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date:        19. March 2015
* $Revision: 	V.1.4.5
*
* Project: 	    CMSIS DSP Library
* Title:		arm_correlate_fast_q15.c
*
* Description:	Fast Q15 Correlation.
*
* Target Processor: Cortex-M4/Cortex-M3
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in
*     the documentation and/or other materials provided with the
*     distribution.
*   - Neither the name of ARM LIMITED nor the names of its contributors
*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @addtogroup Corr
 * @{
 */

/**
 * @brief Correlation of Q15 sequences (fast version) for Cortex-M3 and Cortex-M4.
 * @param[in] *pSrcA points to the first input sequence.
 * @param[in] srcALen length of the first input sequence.
 * @param[in] *pSrcB points to the second input sequence.
 * @param[in] srcBLen length of the second input sequence.
 * @param[out] *pDst points to the location where the output result is written.  Length 2 * max(srcALen, srcBLen) - 1.
 * @return none.
 *
 * <b>Scaling and Overflow Behavior:</b>
 *
 * \par
 * This fast version uses a 32-bit accumulator with 2.30 format.
 * The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit.
 * There is no saturation on intermediate additions.
 * Thus, if the accumulator overflows it wraps around and distorts the result.
 * The input signals should be scaled down to avoid intermediate overflows.
 * Scale down one of the inputs by 1/min(srcALen, srcBLen) to avoid overflow since a
 * maximum of min(srcALen, srcBLen) number of additions is carried internally.
 * The 2.30 accumulator is right shifted by 15 bits and then saturated to 1.15 format to yield the final result.
 *
 * \par
 * See <code>arm_correlate_q15()</code> for a slower implementation of this function which uses a 64-bit accumulator to avoid wrap around distortion.
 */

void arm_correlate_fast_q15(
    q15_t *pSrcA,
    uint32_t srcALen,
    q15_t *pSrcB,
    uint32_t srcBLen,
    q15_t *pDst)
{
#ifndef UNALIGNED_SUPPORT_DISABLE

    q15_t *pIn1;                                   /* inputA pointer               */
    q15_t *pIn2;                                   /* inputB pointer               */
    q15_t *pOut = pDst;                            /* output pointer               */
    q31_t sum, acc0, acc1, acc2, acc3;             /* Accumulators                  */
    q15_t *px;                                     /* Intermediate inputA pointer  */
    q15_t *py;                                     /* Intermediate inputB pointer  */
    q15_t *pSrc1;                                  /* Intermediate pointers        */
    q31_t x0, x1, x2, x3, c0;                      /* temporary variables for holding input and coefficient values */
    uint32_t j, k = 0u, count, blkCnt, outBlockSize, blockSize1, blockSize2, blockSize3;  /* loop counter                 */
    int32_t inc = 1;                               /* Destination address modifier */


    /* The algorithm implementation is based on the lengths of the inputs. */
    /* srcB is always made to slide across srcA. */
    /* So srcBLen is always considered as shorter or equal to srcALen */
    /* But CORR(x, y) is reverse of CORR(y, x) */
    /* So, when srcBLen > srcALen, output pointer is made to point to the end of the output buffer */
    /* and the destination pointer modifier, inc is set to -1 */
    /* If srcALen > srcBLen, zero pad has to be done to srcB to make the two inputs of same length */
    /* But to improve the performance,
     * we include zeroes in the output instead of zero padding either of the the inputs*/
    /* If srcALen > srcBLen,
     * (srcALen - srcBLen) zeroes has to included in the starting of the output buffer */
    /* If srcALen < srcBLen,
     * (srcALen - srcBLen) zeroes has to included in the ending of the output buffer */
    if(srcALen >= srcBLen)
    {
        /* Initialization of inputA pointer */
        pIn1 = (pSrcA);

        /* Initialization of inputB pointer */
        pIn2 = (pSrcB);

        /* Number of output samples is calculated */
        outBlockSize = (2u * srcALen) - 1u;

        /* When srcALen > srcBLen, zero padding is done to srcB
         * to make their lengths equal.
         * Instead, (outBlockSize - (srcALen + srcBLen - 1))
         * number of output samples are made zero */
        j = outBlockSize - (srcALen + (srcBLen - 1u));

        /* Updating the pointer position to non zero value */
        pOut += j;

    }
    else
    {
        /* Initialization of inputA pointer */
        pIn1 = (pSrcB);

        /* Initialization of inputB pointer */
        pIn2 = (pSrcA);

        /* srcBLen is always considered as shorter or equal to srcALen */
        j = srcBLen;
        srcBLen = srcALen;
        srcALen = j;

        /* CORR(x, y) = Reverse order(CORR(y, x)) */
        /* Hence set the destination pointer to point to the last output sample */
        pOut = pDst + ((srcALen + srcBLen) - 2u);

        /* Destination address modifier is set to -1 */
        inc = -1;

    }

    /* The function is internally
     * divided into three parts according to the number of multiplications that has to be
     * taken place between inputA samples and inputB samples. In the first part of the
     * algorithm, the multiplications increase by one for every iteration.
     * In the second part of the algorithm, srcBLen number of multiplications are done.
     * In the third part of the algorithm, the multiplications decrease by one
     * for every iteration.*/
    /* The algorithm is implemented in three stages.
     * The loop counters of each stage is initiated here. */
    blockSize1 = srcBLen - 1u;
    blockSize2 = srcALen - (srcBLen - 1u);
    blockSize3 = blockSize1;

    /* --------------------------
     * Initializations of stage1
     * -------------------------*/

    /* sum = x[0] * y[srcBlen - 1]
     * sum = x[0] * y[srcBlen - 2] + x[1] * y[srcBlen - 1]
     * ....
     * sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen - 1] * y[srcBLen - 1]
     */

    /* In this stage the MAC operations are increased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = 1u;

    /* Working pointer of inputA */
    px = pIn1;

    /* Working pointer of inputB */
    pSrc1 = pIn2 + (srcBLen - 1u);
    py = pSrc1;

    /* ------------------------
     * Stage1 process
     * ----------------------*/

    /* The first loop starts here */
    while(blockSize1 > 0u)
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = count >> 2;

        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        while(k > 0u)
        {
            /* x[0] * y[srcBLen - 4] , x[1] * y[srcBLen - 3] */
            sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum);
            /* x[3] * y[srcBLen - 1] , x[2] * y[srcBLen - 2] */
            sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum);

            /* Decrement the loop counter */
            k--;
        }

        /* If the count is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = count % 0x4u;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            /* x[0] * y[srcBLen - 1] */
            sum = __SMLAD(*px++, *py++, sum);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut = (q15_t) (sum >> 15);
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;

        /* Update the inputA and inputB pointers for next MAC calculation */
        py = pSrc1 - count;
        px = pIn1;

        /* Increment the MAC count */
        count++;

        /* Decrement the loop counter */
        blockSize1--;
    }

    /* --------------------------
     * Initializations of stage2
     * ------------------------*/

    /* sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen-1] * y[srcBLen-1]
     * sum = x[1] * y[0] + x[2] * y[1] +...+ x[srcBLen] * y[srcBLen-1]
     * ....
     * sum = x[srcALen-srcBLen-2] * y[0] + x[srcALen-srcBLen-1] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     */

    /* Working pointer of inputA */
    px = pIn1;

    /* Working pointer of inputB */
    py = pIn2;

    /* count is index by which the pointer pIn1 to be incremented */
    count = 0u;

    /* -------------------
     * Stage2 process
     * ------------------*/

    /* Stage2 depends on srcBLen as in this stage srcBLen number of MACS are performed.
     * So, to loop unroll over blockSize2,
     * srcBLen should be greater than or equal to 4, to loop unroll the srcBLen loop */
    if(srcBLen >= 4u)
    {
        /* Loop unroll over blockSize2, by 4 */
        blkCnt = blockSize2 >> 2u;

        while(blkCnt > 0u)
        {
            /* Set all accumulators to zero */
            acc0 = 0;
            acc1 = 0;
            acc2 = 0;
            acc3 = 0;

            /* read x[0], x[1] samples */
            x0 = *__SIMD32(px);
            /* read x[1], x[2] samples */
            x1 = _SIMD32_OFFSET(px + 1);
            px += 2u;

            /* Apply loop unrolling and compute 4 MACs simultaneously. */
            k = srcBLen >> 2u;

            /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
             ** a second loop below computes MACs for the remaining 1 to 3 samples. */
            do
            {
                /* Read the first two inputB samples using SIMD:
                 * y[0] and y[1] */
                c0 = *__SIMD32(py)++;

                /* acc0 +=  x[0] * y[0] + x[1] * y[1] */
                acc0 = __SMLAD(x0, c0, acc0);

                /* acc1 +=  x[1] * y[0] + x[2] * y[1] */
                acc1 = __SMLAD(x1, c0, acc1);

                /* Read x[2], x[3] */
                x2 = *__SIMD32(px);

                /* Read x[3], x[4] */
                x3 = _SIMD32_OFFSET(px + 1);

                /* acc2 +=  x[2] * y[0] + x[3] * y[1] */
                acc2 = __SMLAD(x2, c0, acc2);

                /* acc3 +=  x[3] * y[0] + x[4] * y[1] */
                acc3 = __SMLAD(x3, c0, acc3);

                /* Read y[2] and y[3] */
                c0 = *__SIMD32(py)++;

                /* acc0 +=  x[2] * y[2] + x[3] * y[3] */
                acc0 = __SMLAD(x2, c0, acc0);

                /* acc1 +=  x[3] * y[2] + x[4] * y[3] */
                acc1 = __SMLAD(x3, c0, acc1);

                /* Read x[4], x[5] */
                x0 = _SIMD32_OFFSET(px + 2);

                /* Read x[5], x[6] */
                x1 = _SIMD32_OFFSET(px + 3);
                px += 4u;

                /* acc2 +=  x[4] * y[2] + x[5] * y[3] */
                acc2 = __SMLAD(x0, c0, acc2);

                /* acc3 +=  x[5] * y[2] + x[6] * y[3] */
                acc3 = __SMLAD(x1, c0, acc3);

            }
            while(--k);

            /* For the next MAC operations, SIMD is not used
             * So, the 16 bit pointer if inputB, py is updated */

            /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
             ** No loop unrolling is used. */
            k = srcBLen % 0x4u;

            if(k == 1u)
            {
                /* Read y[4] */
                c0 = *py;
#ifdef  ARM_MATH_BIG_ENDIAN

                c0 = c0 << 16u;

#else

                c0 = c0 & 0x0000FFFF;

#endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */

                /* Read x[7] */
                x3 = *__SIMD32(px);
                px++;

                /* Perform the multiply-accumulates */
                acc0 = __SMLAD(x0, c0, acc0);
                acc1 = __SMLAD(x1, c0, acc1);
                acc2 = __SMLADX(x1, c0, acc2);
                acc3 = __SMLADX(x3, c0, acc3);
            }

            if(k == 2u)
            {
                /* Read y[4], y[5] */
                c0 = *__SIMD32(py);

                /* Read x[7], x[8] */
                x3 = *__SIMD32(px);

                /* Read x[9] */
                x2 = _SIMD32_OFFSET(px + 1);
                px += 2u;

                /* Perform the multiply-accumulates */
                acc0 = __SMLAD(x0, c0, acc0);
                acc1 = __SMLAD(x1, c0, acc1);
                acc2 = __SMLAD(x3, c0, acc2);
                acc3 = __SMLAD(x2, c0, acc3);
            }

            if(k == 3u)
            {
                /* Read y[4], y[5] */
                c0 = *__SIMD32(py)++;

                /* Read x[7], x[8] */
                x3 = *__SIMD32(px);

                /* Read x[9] */
                x2 = _SIMD32_OFFSET(px + 1);

                /* Perform the multiply-accumulates */
                acc0 = __SMLAD(x0, c0, acc0);
                acc1 = __SMLAD(x1, c0, acc1);
                acc2 = __SMLAD(x3, c0, acc2);
                acc3 = __SMLAD(x2, c0, acc3);

                c0 = (*py);
                /* Read y[6] */
#ifdef  ARM_MATH_BIG_ENDIAN

                c0 = c0 << 16u;
#else

                c0 = c0 & 0x0000FFFF;
#endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */

                /* Read x[10] */
                x3 = _SIMD32_OFFSET(px + 2);
                px += 3u;

                /* Perform the multiply-accumulates */
                acc0 = __SMLADX(x1, c0, acc0);
                acc1 = __SMLAD(x2, c0, acc1);
                acc2 = __SMLADX(x2, c0, acc2);
                acc3 = __SMLADX(x3, c0, acc3);
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut = (q15_t) (acc0 >> 15);
            /* Destination pointer is updated according to the address modifier, inc */
            pOut += inc;

            *pOut = (q15_t) (acc1 >> 15);
            pOut += inc;

            *pOut = (q15_t) (acc2 >> 15);
            pOut += inc;

            *pOut = (q15_t) (acc3 >> 15);
            pOut += inc;

            /* Increment the pointer pIn1 index, count by 1 */
            count += 4u;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pIn2;


            /* Decrement the loop counter */
            blkCnt--;
        }

        /* If the blockSize2 is not a multiple of 4, compute any remaining output samples here.
         ** No loop unrolling is used. */
        blkCnt = blockSize2 % 0x4u;

        while(blkCnt > 0u)
        {
            /* Accumulator is made zero for every iteration */
            sum = 0;

            /* Apply loop unrolling and compute 4 MACs simultaneously. */
            k = srcBLen >> 2u;

            /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
             ** a second loop below computes MACs for the remaining 1 to 3 samples. */
            while(k > 0u)
            {
                /* Perform the multiply-accumulates */
                sum += ((q31_t) * px++ * *py++);
                sum += ((q31_t) * px++ * *py++);
                sum += ((q31_t) * px++ * *py++);
                sum += ((q31_t) * px++ * *py++);

                /* Decrement the loop counter */
                k--;
            }

            /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
             ** No loop unrolling is used. */
            k = srcBLen % 0x4u;

            while(k > 0u)
            {
                /* Perform the multiply-accumulates */
                sum += ((q31_t) * px++ * *py++);

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut = (q15_t) (sum >> 15);
            /* Destination pointer is updated according to the address modifier, inc */
            pOut += inc;

            /* Increment the pointer pIn1 index, count by 1 */
            count++;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pIn2;

            /* Decrement the loop counter */
            blkCnt--;
        }
    }
    else
    {
        /* If the srcBLen is not a multiple of 4,
         * the blockSize2 loop cannot be unrolled by 4 */
        blkCnt = blockSize2;

        while(blkCnt > 0u)
        {
            /* Accumulator is made zero for every iteration */
            sum = 0;

            /* Loop over srcBLen */
            k = srcBLen;

            while(k > 0u)
            {
                /* Perform the multiply-accumulate */
                sum += ((q31_t) * px++ * *py++);

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut = (q15_t) (sum >> 15);
            /* Destination pointer is updated according to the address modifier, inc */
            pOut += inc;

            /* Increment the MAC count */
            count++;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pIn2;

            /* Decrement the loop counter */
            blkCnt--;
        }
    }

    /* --------------------------
     * Initializations of stage3
     * -------------------------*/

    /* sum += x[srcALen-srcBLen+1] * y[0] + x[srcALen-srcBLen+2] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     * sum += x[srcALen-srcBLen+2] * y[0] + x[srcALen-srcBLen+3] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     * ....
     * sum +=  x[srcALen-2] * y[0] + x[srcALen-1] * y[1]
     * sum +=  x[srcALen-1] * y[0]
     */

    /* In this stage the MAC operations are decreased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = srcBLen - 1u;

    /* Working pointer of inputA */
    pSrc1 = (pIn1 + srcALen) - (srcBLen - 1u);
    px = pSrc1;

    /* Working pointer of inputB */
    py = pIn2;

    /* -------------------
     * Stage3 process
     * ------------------*/

    while(blockSize3 > 0u)
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = count >> 2u;

        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            /* sum += x[srcALen - srcBLen + 4] * y[3] , sum += x[srcALen - srcBLen + 3] * y[2] */
            sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum);
            /* sum += x[srcALen - srcBLen + 2] * y[1] , sum += x[srcALen - srcBLen + 1] * y[0] */
            sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum);

            /* Decrement the loop counter */
            k--;
        }

        /* If the count is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = count % 0x4u;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            sum = __SMLAD(*px++, *py++, sum);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut = (q15_t) (sum >> 15);
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;

        /* Update the inputA and inputB pointers for next MAC calculation */
        px = ++pSrc1;
        py = pIn2;

        /* Decrement the MAC count */
        count--;

        /* Decrement the loop counter */
        blockSize3--;
    }

#else

    q15_t *pIn1;                                   /* inputA pointer               */
    q15_t *pIn2;                                   /* inputB pointer               */
    q15_t *pOut = pDst;                            /* output pointer               */
    q31_t sum, acc0, acc1, acc2, acc3;             /* Accumulators                  */
    q15_t *px;                                     /* Intermediate inputA pointer  */
    q15_t *py;                                     /* Intermediate inputB pointer  */
    q15_t *pSrc1;                                  /* Intermediate pointers        */
    q31_t x0, x1, x2, x3, c0;                      /* temporary variables for holding input and coefficient values */
    uint32_t j, k = 0u, count, blkCnt, outBlockSize, blockSize1, blockSize2, blockSize3;  /* loop counter                 */
    int32_t inc = 1;                               /* Destination address modifier */
    q15_t a, b;


    /* The algorithm implementation is based on the lengths of the inputs. */
    /* srcB is always made to slide across srcA. */
    /* So srcBLen is always considered as shorter or equal to srcALen */
    /* But CORR(x, y) is reverse of CORR(y, x) */
    /* So, when srcBLen > srcALen, output pointer is made to point to the end of the output buffer */
    /* and the destination pointer modifier, inc is set to -1 */
    /* If srcALen > srcBLen, zero pad has to be done to srcB to make the two inputs of same length */
    /* But to improve the performance,
     * we include zeroes in the output instead of zero padding either of the the inputs*/
    /* If srcALen > srcBLen,
     * (srcALen - srcBLen) zeroes has to included in the starting of the output buffer */
    /* If srcALen < srcBLen,
     * (srcALen - srcBLen) zeroes has to included in the ending of the output buffer */
    if(srcALen >= srcBLen)
    {
        /* Initialization of inputA pointer */
        pIn1 = (pSrcA);

        /* Initialization of inputB pointer */
        pIn2 = (pSrcB);

        /* Number of output samples is calculated */
        outBlockSize = (2u * srcALen) - 1u;

        /* When srcALen > srcBLen, zero padding is done to srcB
         * to make their lengths equal.
         * Instead, (outBlockSize - (srcALen + srcBLen - 1))
         * number of output samples are made zero */
        j = outBlockSize - (srcALen + (srcBLen - 1u));

        /* Updating the pointer position to non zero value */
        pOut += j;

    }
    else
    {
        /* Initialization of inputA pointer */
        pIn1 = (pSrcB);

        /* Initialization of inputB pointer */
        pIn2 = (pSrcA);

        /* srcBLen is always considered as shorter or equal to srcALen */
        j = srcBLen;
        srcBLen = srcALen;
        srcALen = j;

        /* CORR(x, y) = Reverse order(CORR(y, x)) */
        /* Hence set the destination pointer to point to the last output sample */
        pOut = pDst + ((srcALen + srcBLen) - 2u);

        /* Destination address modifier is set to -1 */
        inc = -1;

    }

    /* The function is internally
     * divided into three parts according to the number of multiplications that has to be
     * taken place between inputA samples and inputB samples. In the first part of the
     * algorithm, the multiplications increase by one for every iteration.
     * In the second part of the algorithm, srcBLen number of multiplications are done.
     * In the third part of the algorithm, the multiplications decrease by one
     * for every iteration.*/
    /* The algorithm is implemented in three stages.
     * The loop counters of each stage is initiated here. */
    blockSize1 = srcBLen - 1u;
    blockSize2 = srcALen - (srcBLen - 1u);
    blockSize3 = blockSize1;

    /* --------------------------
     * Initializations of stage1
     * -------------------------*/

    /* sum = x[0] * y[srcBlen - 1]
     * sum = x[0] * y[srcBlen - 2] + x[1] * y[srcBlen - 1]
     * ....
     * sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen - 1] * y[srcBLen - 1]
     */

    /* In this stage the MAC operations are increased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = 1u;

    /* Working pointer of inputA */
    px = pIn1;

    /* Working pointer of inputB */
    pSrc1 = pIn2 + (srcBLen - 1u);
    py = pSrc1;

    /* ------------------------
     * Stage1 process
     * ----------------------*/

    /* The first loop starts here */
    while(blockSize1 > 0u)
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = count >> 2;

        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        while(k > 0u)
        {
            /* x[0] * y[srcBLen - 4] , x[1] * y[srcBLen - 3] */
            sum += ((q31_t) * px++ * *py++);
            sum += ((q31_t) * px++ * *py++);
            sum += ((q31_t) * px++ * *py++);
            sum += ((q31_t) * px++ * *py++);

            /* Decrement the loop counter */
            k--;
        }

        /* If the count is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = count % 0x4u;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            /* x[0] * y[srcBLen - 1] */
            sum += ((q31_t) * px++ * *py++);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut = (q15_t) (sum >> 15);
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;

        /* Update the inputA and inputB pointers for next MAC calculation */
        py = pSrc1 - count;
        px = pIn1;

        /* Increment the MAC count */
        count++;

        /* Decrement the loop counter */
        blockSize1--;
    }

    /* --------------------------
     * Initializations of stage2
     * ------------------------*/

    /* sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen-1] * y[srcBLen-1]
     * sum = x[1] * y[0] + x[2] * y[1] +...+ x[srcBLen] * y[srcBLen-1]
     * ....
     * sum = x[srcALen-srcBLen-2] * y[0] + x[srcALen-srcBLen-1] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     */

    /* Working pointer of inputA */
    px = pIn1;

    /* Working pointer of inputB */
    py = pIn2;

    /* count is index by which the pointer pIn1 to be incremented */
    count = 0u;

    /* -------------------
     * Stage2 process
     * ------------------*/

    /* Stage2 depends on srcBLen as in this stage srcBLen number of MACS are performed.
     * So, to loop unroll over blockSize2,
     * srcBLen should be greater than or equal to 4, to loop unroll the srcBLen loop */
    if(srcBLen >= 4u)
    {
        /* Loop unroll over blockSize2, by 4 */
        blkCnt = blockSize2 >> 2u;

        while(blkCnt > 0u)
        {
            /* Set all accumulators to zero */
            acc0 = 0;
            acc1 = 0;
            acc2 = 0;
            acc3 = 0;

            /* read x[0], x[1], x[2] samples */
            a = *px;
            b = *(px + 1);

#ifndef ARM_MATH_BIG_ENDIAN

            x0 = __PKHBT(a, b, 16);
            a = *(px + 2);
            x1 = __PKHBT(b, a, 16);

#else

            x0 = __PKHBT(b, a, 16);
            a = *(px + 2);
            x1 = __PKHBT(a, b, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

            px += 2u;

            /* Apply loop unrolling and compute 4 MACs simultaneously. */
            k = srcBLen >> 2u;

            /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
             ** a second loop below computes MACs for the remaining 1 to 3 samples. */
            do
            {
                /* Read the first two inputB samples using SIMD:
                 * y[0] and y[1] */
                a = *py;
                b = *(py + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                c0 = __PKHBT(a, b, 16);

#else

                c0 = __PKHBT(b, a, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                /* acc0 +=  x[0] * y[0] + x[1] * y[1] */
                acc0 = __SMLAD(x0, c0, acc0);

                /* acc1 +=  x[1] * y[0] + x[2] * y[1] */
                acc1 = __SMLAD(x1, c0, acc1);

                /* Read x[2], x[3], x[4] */
                a = *px;
                b = *(px + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                x2 = __PKHBT(a, b, 16);
                a = *(px + 2);
                x3 = __PKHBT(b, a, 16);

#else

                x2 = __PKHBT(b, a, 16);
                a = *(px + 2);
                x3 = __PKHBT(a, b, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                /* acc2 +=  x[2] * y[0] + x[3] * y[1] */
                acc2 = __SMLAD(x2, c0, acc2);

                /* acc3 +=  x[3] * y[0] + x[4] * y[1] */
                acc3 = __SMLAD(x3, c0, acc3);

                /* Read y[2] and y[3] */
                a = *(py + 2);
                b = *(py + 3);

                py += 4u;

#ifndef ARM_MATH_BIG_ENDIAN

                c0 = __PKHBT(a, b, 16);

#else

                c0 = __PKHBT(b, a, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                /* acc0 +=  x[2] * y[2] + x[3] * y[3] */
                acc0 = __SMLAD(x2, c0, acc0);

                /* acc1 +=  x[3] * y[2] + x[4] * y[3] */
                acc1 = __SMLAD(x3, c0, acc1);

                /* Read x[4], x[5], x[6] */
                a = *(px + 2);
                b = *(px + 3);

#ifndef ARM_MATH_BIG_ENDIAN

                x0 = __PKHBT(a, b, 16);
                a = *(px + 4);
                x1 = __PKHBT(b, a, 16);

#else

                x0 = __PKHBT(b, a, 16);
                a = *(px + 4);
                x1 = __PKHBT(a, b, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                px += 4u;

                /* acc2 +=  x[4] * y[2] + x[5] * y[3] */
                acc2 = __SMLAD(x0, c0, acc2);

                /* acc3 +=  x[5] * y[2] + x[6] * y[3] */
                acc3 = __SMLAD(x1, c0, acc3);

            }
            while(--k);

            /* For the next MAC operations, SIMD is not used
             * So, the 16 bit pointer if inputB, py is updated */

            /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
             ** No loop unrolling is used. */
            k = srcBLen % 0x4u;

            if(k == 1u)
            {
                /* Read y[4] */
                c0 = *py;
#ifdef  ARM_MATH_BIG_ENDIAN

                c0 = c0 << 16u;

#else

                c0 = c0 & 0x0000FFFF;

#endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */

                /* Read x[7] */
                a = *px;
                b = *(px + 1);

                px++;;

#ifndef ARM_MATH_BIG_ENDIAN

                x3 = __PKHBT(a, b, 16);

#else

                x3 = __PKHBT(b, a, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                px++;

                /* Perform the multiply-accumulates */
                acc0 = __SMLAD(x0, c0, acc0);
                acc1 = __SMLAD(x1, c0, acc1);
                acc2 = __SMLADX(x1, c0, acc2);
                acc3 = __SMLADX(x3, c0, acc3);
            }

            if(k == 2u)
            {
                /* Read y[4], y[5] */
                a = *py;
                b = *(py + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                c0 = __PKHBT(a, b, 16);

#else

                c0 = __PKHBT(b, a, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                /* Read x[7], x[8], x[9] */
                a = *px;
                b = *(px + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                x3 = __PKHBT(a, b, 16);
                a = *(px + 2);
                x2 = __PKHBT(b, a, 16);

#else

                x3 = __PKHBT(b, a, 16);
                a = *(px + 2);
                x2 = __PKHBT(a, b, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                px += 2u;

                /* Perform the multiply-accumulates */
                acc0 = __SMLAD(x0, c0, acc0);
                acc1 = __SMLAD(x1, c0, acc1);
                acc2 = __SMLAD(x3, c0, acc2);
                acc3 = __SMLAD(x2, c0, acc3);
            }

            if(k == 3u)
            {
                /* Read y[4], y[5] */
                a = *py;
                b = *(py + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                c0 = __PKHBT(a, b, 16);

#else

                c0 = __PKHBT(b, a, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                py += 2u;

                /* Read x[7], x[8], x[9] */
                a = *px;
                b = *(px + 1);

#ifndef ARM_MATH_BIG_ENDIAN

                x3 = __PKHBT(a, b, 16);
                a = *(px + 2);
                x2 = __PKHBT(b, a, 16);

#else

                x3 = __PKHBT(b, a, 16);
                a = *(px + 2);
                x2 = __PKHBT(a, b, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                /* Perform the multiply-accumulates */
                acc0 = __SMLAD(x0, c0, acc0);
                acc1 = __SMLAD(x1, c0, acc1);
                acc2 = __SMLAD(x3, c0, acc2);
                acc3 = __SMLAD(x2, c0, acc3);

                c0 = (*py);
                /* Read y[6] */
#ifdef  ARM_MATH_BIG_ENDIAN

                c0 = c0 << 16u;
#else

                c0 = c0 & 0x0000FFFF;
#endif /*      #ifdef  ARM_MATH_BIG_ENDIAN     */

                /* Read x[10] */
                b = *(px + 3);

#ifndef ARM_MATH_BIG_ENDIAN

                x3 = __PKHBT(a, b, 16);

#else

                x3 = __PKHBT(b, a, 16);

#endif	/*	#ifndef ARM_MATH_BIG_ENDIAN	*/

                px += 3u;

                /* Perform the multiply-accumulates */
                acc0 = __SMLADX(x1, c0, acc0);
                acc1 = __SMLAD(x2, c0, acc1);
                acc2 = __SMLADX(x2, c0, acc2);
                acc3 = __SMLADX(x3, c0, acc3);
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut = (q15_t) (acc0 >> 15);
            /* Destination pointer is updated according to the address modifier, inc */
            pOut += inc;

            *pOut = (q15_t) (acc1 >> 15);
            pOut += inc;

            *pOut = (q15_t) (acc2 >> 15);
            pOut += inc;

            *pOut = (q15_t) (acc3 >> 15);
            pOut += inc;

            /* Increment the pointer pIn1 index, count by 1 */
            count += 4u;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pIn2;


            /* Decrement the loop counter */
            blkCnt--;
        }

        /* If the blockSize2 is not a multiple of 4, compute any remaining output samples here.
         ** No loop unrolling is used. */
        blkCnt = blockSize2 % 0x4u;

        while(blkCnt > 0u)
        {
            /* Accumulator is made zero for every iteration */
            sum = 0;

            /* Apply loop unrolling and compute 4 MACs simultaneously. */
            k = srcBLen >> 2u;

            /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
             ** a second loop below computes MACs for the remaining 1 to 3 samples. */
            while(k > 0u)
            {
                /* Perform the multiply-accumulates */
                sum += ((q31_t) * px++ * *py++);
                sum += ((q31_t) * px++ * *py++);
                sum += ((q31_t) * px++ * *py++);
                sum += ((q31_t) * px++ * *py++);

                /* Decrement the loop counter */
                k--;
            }

            /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.
             ** No loop unrolling is used. */
            k = srcBLen % 0x4u;

            while(k > 0u)
            {
                /* Perform the multiply-accumulates */
                sum += ((q31_t) * px++ * *py++);

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut = (q15_t) (sum >> 15);
            /* Destination pointer is updated according to the address modifier, inc */
            pOut += inc;

            /* Increment the pointer pIn1 index, count by 1 */
            count++;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pIn2;

            /* Decrement the loop counter */
            blkCnt--;
        }
    }
    else
    {
        /* If the srcBLen is not a multiple of 4,
         * the blockSize2 loop cannot be unrolled by 4 */
        blkCnt = blockSize2;

        while(blkCnt > 0u)
        {
            /* Accumulator is made zero for every iteration */
            sum = 0;

            /* Loop over srcBLen */
            k = srcBLen;

            while(k > 0u)
            {
                /* Perform the multiply-accumulate */
                sum += ((q31_t) * px++ * *py++);

                /* Decrement the loop counter */
                k--;
            }

            /* Store the result in the accumulator in the destination buffer. */
            *pOut = (q15_t) (sum >> 15);
            /* Destination pointer is updated according to the address modifier, inc */
            pOut += inc;

            /* Increment the MAC count */
            count++;

            /* Update the inputA and inputB pointers for next MAC calculation */
            px = pIn1 + count;
            py = pIn2;

            /* Decrement the loop counter */
            blkCnt--;
        }
    }

    /* --------------------------
     * Initializations of stage3
     * -------------------------*/

    /* sum += x[srcALen-srcBLen+1] * y[0] + x[srcALen-srcBLen+2] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     * sum += x[srcALen-srcBLen+2] * y[0] + x[srcALen-srcBLen+3] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]
     * ....
     * sum +=  x[srcALen-2] * y[0] + x[srcALen-1] * y[1]
     * sum +=  x[srcALen-1] * y[0]
     */

    /* In this stage the MAC operations are decreased by 1 for every iteration.
       The count variable holds the number of MAC operations performed */
    count = srcBLen - 1u;

    /* Working pointer of inputA */
    pSrc1 = (pIn1 + srcALen) - (srcBLen - 1u);
    px = pSrc1;

    /* Working pointer of inputB */
    py = pIn2;

    /* -------------------
     * Stage3 process
     * ------------------*/

    while(blockSize3 > 0u)
    {
        /* Accumulator is made zero for every iteration */
        sum = 0;

        /* Apply loop unrolling and compute 4 MACs simultaneously. */
        k = count >> 2u;

        /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.
         ** a second loop below computes MACs for the remaining 1 to 3 samples. */
        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            sum += ((q31_t) * px++ * *py++);
            sum += ((q31_t) * px++ * *py++);
            sum += ((q31_t) * px++ * *py++);
            sum += ((q31_t) * px++ * *py++);

            /* Decrement the loop counter */
            k--;
        }

        /* If the count is not a multiple of 4, compute any remaining MACs here.
         ** No loop unrolling is used. */
        k = count % 0x4u;

        while(k > 0u)
        {
            /* Perform the multiply-accumulates */
            sum += ((q31_t) * px++ * *py++);

            /* Decrement the loop counter */
            k--;
        }

        /* Store the result in the accumulator in the destination buffer. */
        *pOut = (q15_t) (sum >> 15);
        /* Destination pointer is updated according to the address modifier, inc */
        pOut += inc;

        /* Update the inputA and inputB pointers for next MAC calculation */
        px = ++pSrc1;
        py = pIn2;

        /* Decrement the MAC count */
        count--;

        /* Decrement the loop counter */
        blockSize3--;
    }

#endif /*   #ifndef UNALIGNED_SUPPORT_DISABLE */

}

/**
 * @} end of Corr group
 */
